How many LEDs ? How fast ?

A project log for WizYasep

LED screen controller over Ethernet... among others ! It's a Wiznet IP controller with a A3P250 FPGA and I/Os.

Yann Guidon / YGDES 12/19/2015 at 22:520 Comments

I often get these questions :

The answer is : a lot !

The W5300 network chip has a 128KB FIFO, that's roughly 40KLED. Is that enough ?

Actually I have reduced the receive FIFO depth to 56KB, or about 19K LED. My largest screen #Mons2015 LED Screen ElectroSuper has 16800 LEDs, and they are spread over 6 WizYasep (2800 LED per sector) so it was easier to keep the size inside a 16 bits word.

Later, on-the-fly picture compression (with #Recursive Range Reduction (3R) HW&SW CODEC ) will increase the LED capacity even more.But I don't think I'll use the whole 128K FIFO because so many LEDs create incredible technical problems at every level and it's easier to just plop another WizYasep (or more).

The answer is : very fast !

Actually the two limiting factors are :

  1. The network speed
  2. The LED string length

The usual asynchronous LEDs (WS2811, WS2812 and similar) are limited to about 30K LED/s. This means a 30K LED string can be refreshed once a second. If you want to refresh at 30Hz, that limits the string to 1000 LEDs. If you want 60Hz, limit your strings to 500 LEDs. With 24 channels, that's 12K LED, well withing the FIFO size.

I have easily run the WizYasep with 20 channels up to about 120Hz with 140 LED per string but the difficulty becomes the generation/storage of all these images (hence my current development of a compression algorithm).

The WizYasep can handle up to 24 channels (and there is provision for 40, and even more) so the next limitation is the network : can you continuously pump 9MB/s over your network link ? That is about 80 strings in parallel at full bandwidth...

So in essence, the WizYasep is "adequate" for most medium and large scale projects, it's easy to use, and the price/performance is above the pack.